Caption: Harmonic wave scattering. Numerical simulation of the wave pattern produced by scattering of a harmonic wave front moving from upper right to lower left past a cylinder. The sequence starts at upper left and finishes at lower right. Here, the wavelength is smaller than the radius of the scattering centre, and a 'shadow' and diffraction pattern form. This simulation is shown as waves moving across a surface, but is based on the differential equations that describe dispersion-free electromagnetic waves. See C014/7192 to C014/7196 for images showing how the pattern changes with wavelength size.